Phosphatase calcineurin

A secondary metabolite produced by Tolypocladium inflation. This fungus was initially isolated in a soil sample collected in Norway. Cyclosporin A is a cyclic undecapeptide. Inside cells, cyclosporine A binds its immunophillin receptor known as cyclophillin. Like the FK506-FKBP12 complex, cyclosporin A-cyclophillin binds and inhibits the protein phosphatase calcineurin. 

Cyclosporine A (CsA) is a water-insoluble cyclic peptide from a fungus composed of 11 amino acids. CsA binds to its cytosolic receptor cyclophilin. The CsA/cyclophilin complex reduces the activity of the protein phosphatase calcineurin. Inhibition of this enzyme activity interrupts antigen receptor-induced activation and translocation of the transcription factor NEAT to the nucleus which is essential for the induction of cytokine synthesis in T-lymphocytes. 

Protein de-phosphorylation Co Imodu I in-stimulated protein phosphatase (Calcineurin)... 

The signaling complex formed around the TCR and the branching pathways that emanate from it resemble the mechanisms used by the growth factors. However, the destinations of these pathways are not all clear. The PLC-y pathway (DAG, IP3, and elevation of intracellular free Ca2+) leads to activation of the phosphatase calcineurin, which activates the transcription factor NF-AT (nuclear factor of activated T cells). This is essential for clonal expansion of T cells because of its pivotal role in the induction of IL-2 expression. NF-AT requires the assistance of the activator protein 1 (AP-1) complex in order to drive expression of IL-2. 

Ca2+ [66], making calcium monitoring a vital tool for cellular biologists. For example, calmodulin-dependent protein phosphatase, calcineurin can be monitored using a probe based on the regulatory domain of the nuclear factor of activated T cells [69], This approach can be taken further to monitor multiple calcium-dependent events in real time [70],... 

Klee, C. B., Ren, H. and Wang, X. Regulation of the calmodulin-stimulated protein phosphatase, calcineurin. /. Biol. Chem. 273 13367-13370,1998. 

Block the phosphatase calcineurin that is involved in the dephosphorylation of dynamin... 

The immune-suppressing drugs tacrolimus (FK 506) and cyclosporin A target the phosphatase calcineurin that is involved in the dephosphorylation of dynamin. It is reported that the uptake of liposomes was significantly decreased after incubation with FK506 (1 pM, 10 minutes prior incubation with liposomes) (1). 

Another drug whose immunosuppressive action is mediated by the complexation with a cellular protein of the immunophilins is FK506. FK506 binds to proteins of the FKBP family. The complex formed is involved in the inhibition of the phosphatase calcineurin, similar to the mode of action of CsA after binding to cyclophilin. The ACE method was used to detect... 

Although it is not chemically related to cyclosporine, tacrolimus (6.7) has a similar mechanism of action. Tacrolimus is an immunosuppressant macrolide antibiotic derived from Streptomyces tsukubaenis. Like cyclosporine, tacrolimus inhibits the same cytoplasmic phosphatase, calcineurin, which catalyzes the activation of a T-cell-specific transcription factor (NF-AT) involved in the biosyntheses of interleukins such as IL-2. Sirolimus (6.8) is a natural product produced by Streptomyces hydroscopicus, it blocks the ability of T cells to respond to cytokines. 

Another Ca receptor is the protein phosphatase calcineurin (see 7.5), which has a specific Ca binding protein as a subunit. 

The protein phosphatase calcineurin was of particular interest since it mediates the immunosuppressive effect of the pharmaceuticals cyclosporin and FK506, often used in organ and tissue transplantations. The biochemical point of application of both pharmaceuticals was unclear for a long time. In initial experiments, it was found that cyclosporin and FK506 bind specifically to two proteins known as cyclophilin and FK506 binding protein, respectively. Both proteins function as peptidyl prolyl cis/trans isome-rases (review Fischer, 1994). 

Another class of transcription-modulating drugs is the immunosuppressants such as cyclosporin A (CsA), which inhibit T cell activation and proliferation, events playing a central role in the immune response and therefore in the inflammatory process. CsA blocks transcriptional induction of cytokines by inhibiting the phosphatase calcineurin, and by the subsequent inhibition of the activation of NF-AT and NF-AT-dependent activation genes. 

Usuda, N., Arai, H., Sasaki, H., Hanai, T., Nagat, T., Muramatsu, T., Kincaid, R. L., and Higuchi, S. 1996. Differential subcellular localization of neural isoforms of the catalytic subunit of calmodulin dependent protein phosphatase (calcineurin) in central nervous system neurons Immunohistochemistry on formalin-fixed paraffin sections employing antigen retrieval by microwave irradiation. J. Histochem. Cytochem. 44 13-18. 

Sustained cytosolic Ca2+ overload usually results in a different route leading to cell death. It mainly relies on the activation of the calcium/calmodulin (CaM)-dependent phosphatase, calcineurin. Calcineurin-catalyzed dephosphorylation promotes apoptosis by regulating the activity of a number of downstream targets, including the pro-apoptotic Bcl-2 family member, Bad (Wang, et al., 1999), and transcription factors of the NFAT (nuclear factor of activated T cells) family (Rao, et al., 1997). There are also other Ca2+-dependent enzymes contributing to the apoptotic events, and they include several DNA-degrading endonucleases (Robertson, et al., 2000) and Ca2+-activated cystein proteases of the calpain family essential for the enzymatic activation of the crucial pro-apoptotic effectors (Altznauer, et al., 2004). 

The expression of genes involved in cell proliferation and cell death is regulated by nuclear transcriptional factors. NFAT (Nuclear Factor of Activated T cells) proteins are a family of Ca2+-dependent transcription factors (Crabtree, 2001), whose nuclear translocation and transcriptional activity is regulated by Ca2+/calmodulin-dependent protein phosphatase, calcineurin (Crabtree, 2001). Thus, NFAT proteins can potentially be activated by diverse stimuli that lead to increased intracellular calcium levels. The NF-kB (nuclear factor kappa B) family... 

The phosphatase calcineurin plays a critical role in many different physiological systems. After the initial elucidation of the central role this enzyme plays in the immune system, it has recendy been implicated in synaptic plasticity and other neuronal processes, in cardiac valve development, and even in cardiac hypertrophy. The later is a disease process for which a calcineurin-regulated pathway may be a good site for therapeutic intervention. In all of these systems, the calcineurin... 

Shibasaki, F., Price, E. R., Milan, D., and McKeon, F. (1996). Role of kinases and the phosphatase calcineurin in the nuclear shuttling of transcription factor NF-AT4. Nature 381, 370—373. 

Early studies reported the lack of stimulation of PLC activity by D2 agonist in the striatum but the measures were taken in striatal slices in which D2 agonists could have very complex effects (Kelly et al., 1988 Pizzi et al., 1988 Rubinstein and Hitzemann, 1990). Mobilization of Ca2+ from intracellular stores by D2 receptor activation has been observed in striatal medium spiny neurons (Hernandez-Lopez et al., 2000). The medium spiny neurons express PLCpl and the D2 receptor activation could stimulate this enzyme by mobilizing Gpy subunits (Hernandez-Lopez et al., 2000). The elevation of intracellular Ca2+ in medium spiny neurons was very transient, since it promoted an immediate closure of L type-Ca2+ channels, due to the activation of the Ca2+-dependent protein phosphatase, calcineurin and subsequent dephosphorylation of the L-type Ca2+ channels (Hernandez-Lopez et al., 2000). 

Ciclosporin is of fungal origin it is a cyclic peptide composed of 11, in part atypical, amino acids. Therefore, orally administered ciclosporin is not degraded by gastrointestinal proteases. InT-helper cells, it inhibits the production of interleukin-2 by interfering at the level of transcriptional regulation. Normally, nuclear factor of activated T cells, (NFAT) promotes the expression of interleu-kin-2. This requires dephosphorylation of the precursor, phosphorylated NFAT, by the phosphatase calcineurin, enabling NFAT to enter the cell nucleus from the cytosol. Ciclosporin binds to the protein cyclophilin in the cell interior the complex inhibits calcineurin, hence the production of interleukin-2. 

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